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Estimating bounds on collisional relaxation rates of spin-polarized 87Rb atoms at ultracold temperatures

by: Mies, F.H.; Williams, C.J.; Krauss, M.; Julienne, P.S.

Publication date: 1996-07

Topics: cold trapped atoms, ab initio calculations, rubidium atom collisions, spin-relaxation rate, spin-spin interactions

Publisher: National Institute of Standards and Technology

Collection: NISTJournalofResearch; NISTresearchlibrary; fedlink; americana

Language: English

Rights: The Journal of Research of the National Institute of Standards and Technology is a publication of the U.S. Government. The papers are in the public domain and are not subject to copyright in the United States. However, please pay special attention to the individual works to make sure there are no copyright restrictions indicated. Individual works may require securing other permissions from the original copyright holder.

Volume: 101

Journal of Research of the National Institute of Standards and Technology

Abstract: We present quantum scattering calculations for the collisional relaxation rate coefficient of spin-polarized Rb-87(f = 2, m = 2) atoms, which determines the loss rate of cold Rb atoms from a magnetic trap. Unlike the lighter alkali atoms, spin-polarized Rb-87 atoms can undergo dipolar relaxation due to both the normal spin-spin dipole interaction and a second-order spinorbit interaction with distant electronic states of the dimer. We present ab initio calculations for the second-order spin-orbit terms for both Rb-2 and Cs-2. The corrections lead to a reduction in the relaxation rate for Rb-87. Our primary concern is to analyze the sensitivity of the Rb-87 trap loss to the uncertainties in the ground state molecular potentials. Since the scattering length for the a(3) Sigma(u)(+), state is already known, the major uncertainties are associated with the X(1) Sigma(g)(+), potential. After testing the effect of systematically modifying the short-range form of the molecular potentials over a reasonable range, and introducing our best estimate of the second-order spin-orbit interaction, we estimate that in the low temperature limit the rare coefficient for loss of Rb atoms from the f = 2,m = 2 state is between 0.4 x 10(-15) cm(3)/s and 2.4 x 10(-15) cm(3)/s (where this number counts two atoms lost per collision). In a pure condensate the rate coefficient would be reduced by 1/2.